Studies of oxidative phosphorylation in the inner membranes of mitochondria in the presence of chlorinated phenols will be complemented by studies on lipid bilayer membranes in order to determine the physico-chemical origin of the toxicity of chloro- phenols. The compounds included in the study have been identified as Designated Hazardous Substances or Consent Decree Pollutants of the Clean Water Act or as Hazardous Constituents in the Resource Conservation and Recovery Act. The project has two parts: (1) Biological, focused on (a) the determination of the 02 consumption rate as a function of the chlorophenol molecular structure, concentration, the pH, and other factors influencing electrostatic interactions; (b) the effect of chlorophenols on proton pumping, and the rate of dissipation of the proton concentration gradient; and (c) on reverse electron transfer. These studies will be done on cells, mitochondria, and submitochondrial particles. (2) Physico-chemical, focused on detailed understanding of the mechanism of action of chlorinated phenols in the lipid matrix of biomembranes. These studies will include: (a) determination of the zeta potential and adsorption isotherms, (b) determination of the pKalpha of chlorophenols adsorbed to membranes, (c) determination of the mechanism of electrical conductivity induced or modified by chlorophenols, (d) determination of changes of boundary potentials which may be related to blocking of 02 consumption, (e) characterization of AHA- complex as the charged membrane-permeable species associated with transmembrane translocation of protons, (f) determination of changes of the gel- to-fluid transition temperature of lipid membranes as a measure of chlorophenol-induced changes of interlipid interaction, and exploration of possible interdigitation and lateral separation of lipids. We expect to identify and characterize at least two types of contributions constituting the toxic action of chlorophenols: (1) protonophoretic, and (2) direct or indirect, mediated by the membrane matrix, interaction of chlorophenols with enzymes in oxidative phosphorylation sequence of reactions.